Techniques for setting up traffic channels in a communications system

ABSTRACT

A control channel supporting traffic control in epochs is divided into two control subchannels each being less than or equal to about a half epoch in duration and occurring serially in time. Slot allocation data may be transmitted and received independently over the subchannels. One subchannel may be used for transmitting forward slot allocation data and the other subchannel may be used for transmitting reverse slot allocation data. The channel split into two subchannels may be a paging channel. The forward and reverse slot allocation data may be transmitted between a base station processor and field unit. Forward and reverse traffic data may be staggered by at least about half an epoch. Transmission of traffic data happens within about two epochs after the assignments.

RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional Application No.60/350,835, filed Jan. 22, 2002, and U.S. application Ser. No.10/350,308, filed Jan. 22, 2003, the entire teachings of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

In a wireless telecommunications system, radio channels provide aphysical link between communications units. The equipment in such asystem typically includes a base station processor in communication witha network such as the Public Switched Telephone Network (PSTN), in thecase of voice communications, or a data network, in the case of datacommunications, and one or more access terminals in communication with aplurality of end user computing devices, such as user PCs. Thecombination of an access terminal and computing device(s) may bereferred to as a field unit. The wireless channels include forwardchannels, for message transmission from the base station processor tothe subscriber access units, and reverse channels, for messagetransmission to the base station processor from the field units.

In the case of a wireless data system such as may be used to providewireless Internet access, each base station processor typically servesmany access terminals, which in turn serve many end user computingdevices. The wireless channels, however, are a limited resource, and aretherefore allocated by a scheduler among the field units served by thebase station processor. The scheduler allocates the wireless channelsamong the field units on a traffic demand basis.

One way of supporting on-demand access among multiple users is referredto as Time Division Multiple Access (TDMA), where each of the wirelesschannels are allocated to specific connections only for certainpredetermined time intervals or time slots. A second way of supportingon-demand access among multiple users is referred to as Code DivisionMultiple Access (CDMA), which allows multiple users to share the sameradio spectrum. Instead of dividing a Radio Frequency (RF) spectrum intonarrow channels (e.g. 30 kHz each in analog wireless systems), CDMAspreads many channels over a broad spectrum (1.25 MHZ in the case of theNorth American CDMA standard known as IS-95). To separate a particularchannel from the other channel using the same spectrum at the same time,a unique digital code called a pseudo-random (i.e., pseudo-noise or PN)code is assigned to each user. Many users (up to 64 for IS-95) share thesame spectrum, each using their unique code, and decoders separate thecodes at each end in a process similar to a tuner that separatesdifferent frequencies in more conventional systems.

The PN codes used for communication channel definitions typically have adefined code repeat period or code epoch. For each such epoch duration(also called a slot), a base station central controlling system orprocessor can further schedule assignments of forward traffic channels(forward slot allocations or “FSAs”) and reverse traffic channels(reverse slot allocations or “RSAs”) to active mobile units for eachepoch. This is typically done in such a way that all channels areassigned to active users as much as possible. It typically takes apredetermined amount of time for the allocation command to be receivedand to configure the demodulators before receiving the new code channel.In particular, when a PN code is reassigned to a different userconnection, it typically takes a determined period of time for the codedemodulators in the receiver to lock in the new code. This in turnintroduces latency in the reception of the data packets that must travelon the coded channel.

To coordinate traffic channels, the base station processor communicateswith a given field unit in the following manner. First, the base stationprocessor checks to make sure there is an available channel. Second, thebase station processor sends a message to the given field unit to set upthe available channel. The given field unit processes the message (2-3epochs) to set-up the channel and sends an acknowledgment (1-2 epochs)confirming set-up complete. To tear down the channel, the base stationprocessor sends a message to the given field unit, which processes thecommand (1-2 epochs) and sends back an acknowledgment (1-2 epochs).

SUMMARY OF THE INVENTION

A communications system employing the principles of the presentinvention reduces packet latency, which, in turn, improves response timefor setting up traffic channels in a communications system, such as anon-demand access, packet switched, CDMA communications system. Theseimprovements apply to both forward and reverse traffic channels.

Channel code assignments are pipelined from a base transceiver station(BTS) down to all of the mobile units in a cell zone associated with theBTS so the actual transmission of traffic data can begin, within abouttwo epochs after the channel assignments. Keeping this delay to aminimum is what improves the latency.

There are at least three features that help in keeping this delay short:(i) dividing a control channel, such as the paging channel, into controlsubchannels, such as two control subchannels or half-channels(optionally referred to as a forward half-channel and reversehalf-channel), where, in the case of two control subchannels, the newsplit paging channels may be less than or equal to about half theduration of the standard control channels (e.g., half an epoch), (ii)staggering the forward and reverse traffic channels by about half anepoch, and eliminating the acknowledgment returned to the BTS, since theslot allocation/deallocation commands are redundant (i.e., sent multipletimes for a contiguous slot allocation). Forward and reverse slotallocation data may be transmitted in objects less than or equal toabout a half epoch duration and transmitted from the base stationprocessor to the field units in respective forward and reversesubchannels, e.g., paging subchannels.

These two features can improve latency by one or two epochs per forwardand reverse channel allocation. This, in turn, shows up as a noticeableimprovement in response time to the user.

In one embodiment, the present invention may be used in link layersoftware on the base station and field units to improve channel latencyand can be used by any system using a CDMA packet switchedcommunications system.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 is a block diagram of a wireless communications system suitablefor performing wireless paging channel techniques described herein;

FIG. 2 is a timing diagram of a technique for allocating a forwardchannel according to the principles of the present invention used in thesystem of FIG. 1;

FIG. 3 is a timing diagram of a technique for allocating a reversechannel according to the principles of the present invention used in thesystem of FIG. 1; and

FIG. 4 is a timing diagram of an alternative technique for allocatingthe reverse channel according to the principles of the present inventionused in the system of FIG. 1.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A description of preferred embodiments of the invention follows.

FIG. 1 shows a wireless telecommunications system suitable for reducingpacket latency according to the principles of the present invention. Aplurality of data processing devices, such a personal computers (PCs),Personal Digital Assistants (PDAs), data enabled mobile phones or thelike (collectively the PCs) 12 a-12 e are in communication with a subsetof access terminals (ATs) 14 a-d via a wired connection 20. The wiredconnection 20 typically conforms to a wired protocol such as Ethernetwith embedded TCP/IP or UDP/IP packets. The combination of a PC 12 andAT 14 may be referred to as a field unit 15 or remote unit. In the caseof the second field unit 15 b, the PC associated with the AT 14 b isbuilt into the AT 14 b and is therefore not shown.

The field units 16 a-15 d are in wireless communication with a basestation processor (BSP) 16 via a wireless link 26. The wireless link 26conforms to a wireless protocol such as IS-95 or another wirelessprotocol which supports communications via an RF medium.

The base station processor 16 is also connected to a public accessnetwork 18, such as the Internet, via an internetworking gateway 24. Theinternetworking gateway 24 is typically a bridge, router, or otherconnection to a network backbone and may be provided by a remoteprovider, such as an Internet Service Provider (ISP). In this manner, anend user at the PC 12 is provided a wireless connection to a publicaccess network 18 via the AT 14 and the base station processor 16.

Typically, a user PC 12 sends a message over a wired link 20, such as alocal area network or bus connection, to the field unit 15. The fieldunit 15 sends a message via the wireless link 26 to the base stationprocessor 16. The base station processor 16 sends the message to thepublic access network 28 via the internetworking gateway 18 for deliveryto a remote node 30 located on the network 28. Similarly, the remotenode 30 located on the network can send a message to the field unit 15by sending it to the base station processor 16 via the internetworkinggateway 24. The base station processor 16 sends the message to theaccess terminal 14 serving the PC 12 via the wireless link 26. Theaccess terminal 14 sends the message to the PC 12 via the wired link 20.The PC 12 and the base station processor 16 can therefore be viewed asendpoints of the wireless link 26.

As indicated above, there are typically many more field units 15 thanthere are available wireless channel resources. For this reason, thewireless channels are allocated according to some type of demand-basedmultiple access technique to make maximum use of the available radiochannels. Multiple access is often provided in the physical layer or bytechniques that manipulate the radio frequency signal, such as TimeDivision Multiple Access (TDMA) or Code Division Multiple Access (CDMA)techniques. In any event, the nature of the radio spectrum is such thatit is a medium that is expected to be shared. This is quite dissimilarfrom the traditional wired environment for data transmission in which awired medium, such as a telephone line or network cabling, is relativelyinexpensive to obtain and to keep open all the time.

In a typical wireless transmission, a send message often results in areturn acknowledgment message. A wireless channel is allocated to sendthe message, and a second wireless channel is allocated in the oppositedirection to send the return message. Wireless channel allocation canoccur by a variety of methods well known in the art.

FIG. 2 is a timing diagram 30 indicating latency improvements (i.e.,reductions) for allocating the forward channels of the wireless system10. This improvement is described for a packet switched CDMAcommunications system but may be used to reduce latency in TDMA or othermultiplexing systems that have forward slot allocations. In the presentCDMA case, the forward link—from base station processor 16 to fieldunits 15—includes a paging channel, multiple traffic channels, andmaintenance channels. The timing diagram 30 includes relative timing ofsignals in the paging and traffic channels.

The timing diagram 30 is separated horizontally into four epochs 32-1through 32-4 and vertically into a sequence of steps used to transmitand activate the forward channels. A first step 34 is provided in whichthe base station processor 16 loads forward slot allocations into apaging/F buffer object. The paging/F buffer object includes typicaloverhead information as a standard buffer object of the prior art, butonly includes traffic channel allocation data for the forward trafficchannels and, thus, is only a half epoch in duration. A second step 36is provided in which the paging/F buffer object is transmitted by thebase station processor 16 to the field unit 15 and demodulated by thefield unit 15. In a third step 38, the field unit 15 decodes thepaging/F buffer object, extracts forward channel assignments, andconfigures its receiver(s) for the forward channels. In a fourth step40, a half epoch after decoding the paging/F buffer object, the fieldunit 15 decodes data traffic on the forward channels.

The paging channel may be split into two subchannels, such as one fortransmitting forward slot allocation data and one for transmittingreverse slot allocation data. Each subchannel may be less than or equalto about half an epoch long and may be referred to as a “forward”half-channel and a “reverse” half-channel.

It should be understood that the paging channel may be furthersubdivided into smaller slotted subchannels of less than or equal toabout 1/n.sup.th of an epoch long, where n is the number of subchannels.Further, the lengths of the subchannels may be different, so long as thecombined length is less than or equal to an epoch. It should also beunderstood that the subdivided channel may be a channel other than thepaging channel, such as a maintenance channel or an unused trafficchannel.

The rest of the discussion assumes the paging channel is split into twosubchannels, referred to as half-channels.

As shown in FIG. 2, step 36, the forward paging/F object loaded in thefirst epoch 32-1 is transmitted over the first half-channel in the firsthalf epoch of epoch 32-2 and also demodulated in the same first half ofthe epoch 32-2. The second half of the epoch 32-2 is used by the fieldunit 15 to decode the slot allocation data, sent in the form of messagesor control data, and to configure the forward traffic channels. Thismeans the forward channel assignments can be placed into the forwardhalf-channel one epoch (e.g., epoch 32-2) and the forward traffic canthen be placed into the very next epoch (e.g., epoch 32-3). This saves awhole extra epoch in time that would normally be needed to demodulate astandard, full paging channel, buffer object, which would, for example,fill the entire epoch 32-2 and not be ready for forward traffic datauntil two epochs later, epoch 32-4.

FIG. 3 is a timing diagram 50 indicating latency improvements (i.e.,reductions) for allocating the reverse channels of the wireless system10. The forward epochs 32 and a corresponding set of reverse epochs 52are provided to show timing relationships between the forward andreverse directions. The process defined in FIG. 3 includes reversepaging/R steps 54 a-60 that parallel the forward paging/F steps 34-40provided in FIG. 2.

Referring to FIG. 3, as discussed above, the paging channel is splitinto two half-channels. The first half-channel may be used fortransmitting the ½ size paging/F object (as discussed above), and thesecond half-channel may be used for transmitting a ½ size paging/Robject. For reverse traffic, the ½ size paging/R objects containsoverhead data of standard objects, as in the case of the ½ size paging/Fobjects, and, similarly, the ½ size paging/R objects also include theReverse Slot Allocation (RSA) data that can be sent and demodulated inthe second half-epoch of the second epoch 32-2. Compare step 36 withstep 56 to see the timing relationship of the forward and reversehalf-channels.

The reverse epoch 52 may be staggered by half an epoch to close up theamount of delay between sending Reverse Slot Allocations (step 56) andactually transmitting reverse traffic (step 60). This means the reversechannel assignment can be transmitted in the reverse half-channel in oneepoch 52-2 and, in the following epoch 52-3, reverse traffic data can besent up the reverse channel defined by the reverse slot allocation data.

Splitting the paging channel into two channels of half-epoch durationand independently transmitting the paging/F and paging/R objects savesan extra epoch in time that would normally be needed to demodulate afull, standard, paging channel having the paging/F and paging/R objectsconcatenated and transmitted together in a full epoch. Also, by makingthe paging/R object only ½ epoch, the base station processor 16 candelay loading the Reverse Slot Allocations by half an epoch (e.g., startthe loading at the start of the first reverse epoch 52-1 rather than atthe start of the first forward epoch 32-1), which allows late requestsget into the allocations that normally would need to wait another epoch.

This system can be improved even further if the base station processor16 delays the loading of the Reverse Slot Allocations 54 a until afterthe first forward epoch 32-1, as defined by a loading step 54 b in thetiming diagram 50 of FIG. 4.

It is assumed that the Slot allocations arrive at the physical layer andare sent between the base station processor 16 and field unit 15 in oneepoch. This results in another one-half epoch improvement on latencyoverall.

It should be understood that the process described herein may beprovided by software, firmware, or hardware. The software may be storedin RAM, ROM, optical or magnetic disk, or other storage media. Thesoftware is loaded and executable by a processor that interacts withdevices capable of providing wire or wireless communication functionsdescribed herein or known to operate in the system 10 of FIG. 1. Thesoftware may be distributed by physical or wireless distribution methodscommonly used in commerce.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. A field unit comprising: a receiver for receiving a control channeldivided into a first control subchannel of less than or equal to about ahalf epoch in duration and a second control subchannel of less than orequal to about a half epoch in duration, the second control subchannelindependent of the first control subchannel; a processor for extractinga reverse channel assignment; and a transmitter for transmitting reversetraffic data using said reverse channel assignment.
 2. The field unit ofclaim 1, wherein the control channel is a paging channel.
 3. The filedunit of claim 1, wherein said first control subchannel includes forwardchannel assignments.
 4. The field unit of claim 3, wherein said secondcontrol subchannel includes said reverse channel assignments.
 5. Thefield unit of claim 1, wherein said processor processes reverse trafficdata within about a next epoch after extracting said reverse channelassignment.
 6. The field unit of claim 3, wherein said processorextracts a forward channel assignment from said first controlsubchannel.
 7. The field unit of claim 6, wherein said processorprocesses forward traffic data within about a next epoch.
 8. A methodfor traffic channel setup in a field unit comprising: receiving acontrol channel divided into a first control subchannel of less than orequal to about a half epoch in duration and a second control subchannelof less than or equal to about a half epoch in duration, the secondcontrol subchannel independent of the first control subchannel;extracting a reverse channel assignment; and transmitting reversetraffic data using said reverse channel assignment.
 9. The method ofclaim 8, wherein the control channel is a paging channel.
 10. The methodof claim 8, wherein said first control subchannel includes forwardchannel assignments.
 11. The method of claim 10, wherein said secondcontrol subchannel includes said reverse channel assignments.
 12. Themethod of claim 8, further comprising processing said reverse trafficdata within about a next epoch after extracting said reverse channelassignment.
 13. The method of claim 10, further comprising extracting aforward channel assignment from said first control subchannel.
 14. Themethod of claim 11, further comprising processing forward traffic datawithin about a next epoch.